In many sensor applications, there is a need for power to operate associated electrical components yet it is often inconvenient, due to maintenance issues, or impossible due to space and mass limitations, to provide this power by conventional means such as batteries or combustion processes. In this light it would be advantageous to be able to realize a compact miniaturized power harvesting systems that could glean ambient power, i.e. power stored in local vibrations, and convert this into useful electricity. It would also be advantageous if the same technology that generated the power could be used as a sensor since such could greatly simplify the sensor design and reduce the overall package size.
Applications for such technology might include a remotely distributed after-market sensor suite that could be employed on a vibrating machine to provide self-powered sensors for sensing as well as communications via RF transmission with power for the transmission coming from conversion of vibrations to power. Such an arrangement would be very convenient from an installation and maintenance point of view. Structural health monitoring using a distributed sensor network that is not only independently powered but which can also independently report, if conditions should warrant, could be possible by employing such technology.
A power-harvesting device of this type could also be used in geophysical prospecting or as an alarm/data recorder for natural geophysical events. In the prospecting case, the vibrational energy from an energy source such as a vibrator could be converted to electrical energy and used to power RF transmission of data. This would simplify the distribution of seismic recording devices since it would remove the need for cabling. Such a system could also include a GPS receiver so that the step of surveying could also be eliminated from geophone placement during land surveys. Power to operate the device could also come from the vibrations associated with physically carrying the device and deploying it on the survey site as well as the energy generated from seismic waves. In the case of geophysical event monitoring, an array of geophones could be placed remotely around a likely event epicenter and begin transmitting information at the occurrence of an event. By eliminating batteries from the transmission system, these sensors can be made inexpensively.
Such a system could also be used as an alarm in military or security applications where the generated power from the vibration of military or other vehicles could wake up the sensor and allow for a warning transmission. Such devices could also be used to power pacemakers or other invasive health monitoring or health support systems where power could be generated from the motion of the wearer. In all of these applications, a study of the vibrational spectrum and/or waveform could also be used to provide information about the health of the system or to identify a particular event or even a particular vehicle.
Another potential application concerns tires and sensors for tires. In many in-tire sensor suits there is a recognized need for continuous data transmission. This need arises for safety and performance reasons. For example, while temperature and pressure may change slowly during the course of normal operation, one of the real benefits of in-tire temperature and pressure monitoring is to alert the driver to potential catastrophic failures before they occur. Such failure events can develop very rapidly at high speeds; hence a need exists for more continuous monitoring. U.S. Pat. No. 5,749,984 (Frey et al.) discloses a tire monitoring system and method that is capable of determining such information as tire deflection, tire speed, and number of tire revolutions. Another example of a tire electronics system can be found in U.S. Pat. No. 4,510,484 (Snyder), which concerns an abnormal tire condition warning system. U.S. Pat. No. 4,862,486 (Wing et al.) also relates to tire electronics, and more particularly discloses an exemplary revolution counter for use in conjunction with automotive and truck tires.
Further there is a recognized benefit in allowing vehicle tires to act as real-time sensors that interact with a number of vehicle control systems, such as anti-lock braking systems (ABS), steering, and traction control. In such applications it is critical that information be transmitted continuously and with minimum temporal bias to the relevant control system. Such requirements force the consideration of continuous data transmission and methods of powering continuous data transmission devices. A typical solution for powering tire electronics systems corresponds to the use of a non-rechargeable battery, which inherently provides an inconvenience to the tire user since proper electronics system operation is dependent on periodic battery replacement. Conventional batteries also often contain heavy metals that are not environmentally friendly and which present disposal concerns, especially when employed in significant quantities. Still further, batteries tend to deplete their energy storage quite rapidly when powering electronic applications characterized by complex levels of functionality. Battery storage depletion is especially prevalent in electronic systems that transmit information over a relatively far distance such as from truck wheel locations to a receiver in the truck cabin. In such considerations, it is readily apparent that batteries are undesirable for many reasons. Therefore it would be a major advance in the art to find a means of scavenging power from vibration and deformation sources intrinsic to the tire.
Yet another potential capability offered by electronics systems integrated with tire structures corresponds to asset tracking and performance characterization for commercial vehicular applications. Commercial truck fleets, aviation crafts and earthmover/mining vehicles are all viable industries that could utilize the benefits of self-powered tire electronic systems and related information transmission. Self-powered sensors could determine the distance each tire in a vehicle has traveled and thus aid in maintenance planning for such commercial systems. Vehicle location and performance can be optimized for more expensive applications such as those concerning earth-mining equipment. Entire fleets of vehicles could be tracked using RF tag transmission, exemplary aspects of which are disclosed in U.S. Pat. No. 5,457,447 (Ghaem et al.).
Such integrated tire electronics systems have conventionally been powered by a variety of techniques and different power generation systems. Examples of mechanical features for generating energy from tire movement are disclosed in U.S. Pat. No. 4,061,200 (Thompson) and U.S. Pat. No. 3,760,351 (Thomas). Such examples provide bulky complex systems that are generally not preferred for incorporation with modern tire applications. Yet another option for powering tire electronics systems is disclosed in U.S. Pat. No. 4,510,484 (Snyder), which concerns a piezoelectric reed power supply symmetrically configured about a radiating centerline of a tire.
It is appreciated that certain advantages of piezoelectric materials have long been recognized. However, such technology is constantly improving, thus potentially affording applications that utilize piezoelectric materials with improved operating capabilities. Examples of relatively new advances in piezoelectric technology are provided in U.S. Pat. Nos. 5,869,189 (Hagood, IV et al.) and 6,048,622 (Hagood, IV et al.), directed to composites for structural control. The presently disclosed technology concerns further advances in piezoelectric technology such that a piezoelectric power generating device can be miniaturized for purposes of energy harvesting and, in certain circumstances concurrently function as sensors and together can be integrated with virtually any vibration generating device or structure to provide self-powered systems and devices.
The disclosures of all of the foregoing United States patents are hereby fully incorporated into this application for all purposes by reference thereto. While various power generation systems have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.